Seems like this has been resolved; however, just let me add that the Marineland slimline 15 does a great job on my 10 gallon tank. I doubled up on tank size ratings for 2 of my other tanks and now regret it. The flow is way too strong.

One of the great myths in the hobby is that you need 4x to 10x the tank size in GPH (gallons per hour) flow for adequate filtration. It would seem to make sense since if a little is good, a lot must be better...NOT. What we really want is to filter water more slowly through very fine filtering media that will capture even the smallest particulate matter.
If you think it through, if your filter is filtering the water very well, how many times per hour does each drop need to be filtered. It seems to me that 2x - 4x is more than enough.

Some folks, especially folks with messy fish, use high flow filters and/or power heads to attempt to capture any/all detritus in the tank. I'll admit that a pristine tank may look better, but it's not natural and is often a detriment to the health of the tank and the fish. On top of that, detritus in the filter is more quickly converted to dissolved organics which pollutes the water more than a slow decomposition in the substrate mulm.

But I digress...I suggest using a filter that is rated for the size of the tank. If choosing a new filter, consider a filter that allows you to choose the type and volume of filter media.
Service the filter regularly to remove detritus and use a very fine media in the last stage to polish the water.

edit: One last thought... consider feeding fish less with high quality foods that produce less waste.

One of the reasons some systems need a higher turnover rate than others has to do with the volume of media the filter holds. The higher the turnover rate the lower the ammonia concentration that has to be processed. Because HOBs and internal filters don't house as much media, they need a lower concentration in order to process the waste. Canisters don't need as high of a turnover rate because they hold significantly more media, meaning that they can process more ammonia in one pass through the filter.

If anything, slower flow rates are more conducive to the formation of beneficial nitrosomona and nitrobacter bacteria colonies and the processing of ammonia and nitrite. And there is far more beneficial biology in the substrate than most filters, especially cartridge filters with little/no bio-media.
There is no evidence that I'm aware of that suggests that high volume, faster flow rates improves de-nitrification.

The fallacy of faster flow rates is that more detritus will be captured in the filter. We don't need to move more water....we need to filter/purify the water better.

Yes, I should have more correctly referred to the early N2 stages of the nitrogen cycle where aerobic nitrosomonas bacteria convert ammonia to nitrite and aerobic nitrobacter bacteria convert nitrite into nitrate. Denitrification is when anaerobic bacteria completes the N2 cycle extracting O2 from nitrates releasing nitrogen gas. Short of special media filters and/or deep sand beds, denitrification does not typically occur in most home aquariums.

The point I was suggesting was that higher filter flow rates are not a positive factor in processing ammonia and/or nitrites.

It really depends on the type of tank you run. I used to go by the manufacturers ratings, but after beefing up the filtration systems I would never go back. My fish are healthier and the tanks are significantly cleaner. It's fantastic - I never have to vacuum and I don't have to clean the filters more than twice a year. I have never had such beautiful tanks with so little work.

That's my experience on the matter - surely yours is as different from mine as the tanks we keep.